Part of the answer of course is that they did, but stopped. And there has to be a reason behind that failure to develop better tech. Not any conspiracy, but a nice cosy relationship between the big auto and big oil, the fact that refining is easier than retooling, and a desire to make as many dollars as possible.
Why are the big auto companies still not serious about making good EVs? That, in a nutshell, is the question. But when the fastest, highest-accelerating car in the world is powered by batteries and an electric motor, and the most economical and clean in terms of pollution produced per mile are electric, it sometimes seems there's a conspiracy to pollute as much of the Earth as possible and see how many people die off, doesn't it?
Not helping are the pathetic lame-arsed piles of crap the auto companies are trying to lead off with, starting with Toyota's much-vaunted Prius which is really not that much of an advance over most any small economical petrol-engined car.
Why do I say that? Because to be really serious, Toyota should have led off not with a stupid petrol-engined car that uses electric power like some kind of glorified clock spring reservoir, but a diesel car with plug-in electric capability right from the start. As we've just seen, despite their protestations, the damn technology IS TOO there, and has been for decades.
And a huge part of the reason is (get braced for it) - US, dear people. If you dug your heels in and asked at the dealer for a car that's able to run on electric rechargeable power and relatively clean biodiesel at need, then by now that vehicle would exist. But by buying "one more while I'm waiting for the new clean vehicles" we're all contributing to the feet-dragging. A bit like "aw, just one more cigarette," really... And meanwhile, we're shortening the lifespans and reducing the living standards of our children and grandchildren, and working on leaving a many generations legacy of the not-so-good kind behind us...